The 2007 CLS55 AMG with the M113K supercharged V8 is a formidable performance sedan, but the engine has catastrophic weakness with piston ring failures and balance shaft gear issues that can destroy motors without warning. Transmission oil cooler leaks and mount failures are also frequent issues that require attention.
Catastrophic Piston Ring / Bore Scoring Failure
Common · high severity
Typical onset: 70,000-130,000 mi
Symptoms: Excessive oil consumption (1+ quart per 500-1000 miles), Blue smoke on cold start or acceleration, Loss of compression leading to misfires, Metal debris in oil, Complete engine seizure in worst cases
Fix: M113K engines suffer from inadequate piston ring tension and poor cylinder wall treatment. Pistons rock in bores, glazing cylinders and causing ring flutter. Requires complete engine rebuild with block resurfacing or liner installation, upgraded piston rings, new pistons. Many opt for full short block replacement. 35-50 labor hours depending on approach.
Estimated cost: $12,000-22,000
Balance Shaft Gear Failure
Occasional · high severity
Typical onset: 80,000-150,000 mi
Symptoms: Sudden metallic rattling or knocking from deep in engine, Metal shavings in oil, Check engine light with cam/crank correlation codes, Catastrophic engine damage if gear teeth shear
Fix: The balance shaft drive gears on M113K can strip teeth or fail, sending metal through the entire engine. Requires complete engine disassembly, replacement of balance shaft assembly, timing components, and inspection of all oil galleries for debris. Often discovered during rebuild for other issues. 40-55 hours if caught early, totaled engine if teeth circulate.
Estimated cost: $8,000-15,000
Transmission Oil Cooler Line Leaks
Common · medium severity
Typical onset: 60,000-120,000 mi
Symptoms: Transmission fluid puddles under vehicle, Burnt transmission fluid smell, Slipping or harsh shifts from low fluid, Red/brown fluid visible on cooler lines at radiator
Fix: The 722.6 transmission cooler lines and connections at the radiator corrode and leak. Lines run along frame rails and are exposed to road salt. Requires replacement of metal lines and/or rubber hoses, plus fluid flush. 3-5 hours labor depending on which sections fail.
Estimated cost: $800-1,500
Transmission Mount Failure
Common · low severity
Typical onset: 70,000-110,000 mi
Symptoms: Clunk when shifting from Park to Drive or Reverse, Vibration at idle in gear, Excessive driveline movement felt through chassis, Visible separation or tearing of rubber mount
Fix: The large transmission mount deteriorates from the stress of 510 lb-ft torque and supercharger heat. Rubber separates from metal backing. Replacement requires supporting transmission and removing bolts from crossmember. 2-3 hours labor.
Estimated cost: $400-700
Supercharger Snout Bearing / Coupler Failure
Occasional · medium severity
Typical onset: 90,000-140,000 mi
Symptoms: Whining or grinding noise from front of engine, Supercharger squeal that changes with RPM, Loss of boost pressure, Metal shavings in supercharger oil
Fix: The Eaton M113 supercharger input shaft bearing and rubber coupler wear out. Bearing failure sends metal into the blower. Requires removal of supercharger, replacement of snout bearings, coupler, and often full supercharger rebuild or replacement. 8-12 hours labor.
Estimated cost: $2,500-4,500
Airmatic Suspension Strut Leaks
Common · medium severity
Typical onset: 80,000-130,000 mi
Symptoms: Vehicle sits low on one or more corners, Airmatic warning on dash, Compressor runs excessively, Visible oil residue on strut bodies
Fix: Airmatic air struts develop leaks in the rubber bladder or seals. Front struts more common than rear. Requires strut replacement (no rebuild option from MB). Compressor often also worn from overwork. 4-6 hours for pair of fronts or rears.
Estimated cost: $2,000-3,500
Fuel Pump and Sender Unit Failure
Occasional · medium severity
Typical onset: 90,000-150,000 mi
Symptoms: No-start or crank/no-start condition, Fuel gauge reading erratically or stuck, Stumbling or hesitation under hard acceleration, Whining noise from fuel tank area
Fix: Fuel pump assemblies fail from age and ethanol fuel degradation. The CLS has a large saddle tank requiring access through rear seat area. Requires dropping tank or accessing through service panel, replacing entire pump/sender assembly. 4-5 hours labor.
Estimated cost: $1,200-2,000
Owner tips
Check oil consumption religiously every 500 miles - catch bore scoring early before catastrophic failure
Use quality synthetic 0W-40 oil and change every 5,000 miles maximum to extend engine life
Inspect transmission cooler lines annually for seepage - preventive replacement at 80k saves a transmission
Budget $2,000-3,000 annually for deferred maintenance and surprise repairs on a 17-year-old AMG
Pre-purchase inspection MUST include compression test, leakdown test, and oil analysis - many engines are ticking time bombs
Only buy if you can afford a $15k-20k engine rebuild or have already confirmed this specific engine has been rebuilt with upgraded components - otherwise you're gambling with a grenade.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.
Fitment notes: Battery located in trunk; high-performance AGM required for supercharged V8
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Every control module on the 2006-2008 Mercedes-Benz CLS55 AMG — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
⚠️ Controls power seat, memory, heating/ventilation. Basic adaptation usually sufficient.
Fuel Pump Control Module (FPCM)0.5 hr R&Rrelearn only +0.2 hr▸ programming details
📍 Trunk, right side panel or integrated into SAM-R
🔧 Star Diagnosis or Autel
⚠️ May be integrated into SAM-R on some production dates; verify before ordering. Fuel pressure adaptation recommended.
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2007 Mercedes-Benz CLS55 AMG 5.4L Supercharged V8 and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years.